1. Field of the Invention
The present invention relates to a perovskite catalyst composed of perovskite oxide that is used as an exhaust gas purifying catalyst, a photocatalyst, or other types of catalyst, and a method of manufacturing the perovskite catalyst.
2. Description of the Related Art
The perovskite catalyst is used as an exhaust gas purifying catalyst that purifies exhaust gas of a diesel engine, a photocatalyst that decomposes water into hydrogen and oxygen using optical energy, and the like. In general, the perovskite catalyst is composed of perovskite oxide represented by the general equation ABO3. For example, a perovskite catalyst is known that contains a rare earth element such as La or an alkaline earth element such as Sr at the A-site and contains various transition elements at the B-site.
The perovskite oxide is obtained by an A-site material and a B-site material being mixed and fired. The A-site material includes an element composing the A-site and the B-site material includes an element composing the B-site.
In recent years, it has been required to develop a perovskite catalyst having higher activity. Therefore, studies are being conducted regarding atomizing perovskite oxide, increasing specific surface area, and the like.
For example, JP-A-2002-321923 discloses a method of manufacturing perovskite represented by LaRuO3. Here, perovskite oxide that has been fired is ground and atomized.
JP-A-2003-260356 discloses an H-type layer perovskite photocatalyst that uses a compound having an Aurivillius structure having a structure similar to ion-exchanging layered perovskite. The compound is acid-treated and adjusted. Here, various kinds of cations can be present at the B-site of the perovskite oxide expressed by the general formula ABO3.
JP-A-H9-267040 discloses an exhaust gas purifying catalyst composed of perovskite oxide that burns soot within the exhaust gas at a low temperature. According to the disclosure, synthesis conditions are adjusted, thereby obtaining perovskite oxide that is expressed by a formula AXA′1−XBYB′1−YO3 (where, A is La; A′ is at least one selected from Sr and Ca; B is at least one selected from Fe and Y; B′ is at least one selected from Fe, Zn, and Mg; 0.5<x≦1 and 0.5<y≦1.0).
However, in the method in which the perovskite oxide catalyst powder is ground after firing, the perovskite structure may be destroyed by grinding and catalytic activity may decrease.
In addition, in the method in which acid treatment is performed on the perovskite oxide, the catalytic structure may be destroyed and catalytic activity may decrease.
Moreover, in the method in which the synthesizing conditions are adjusted and the perovskite oxide expressed by the formula AXA′1−XBYB1−YO3 is obtained, although the specific surface area of the catalyst itself increases, catalytic sites may decrease when the catalyst is, for example, carried by a carrier.